A train, an automobile, or an air conditioner, for example, is mounted with a DC power supply unit that converts an AC voltage to a DC voltage. The DC power supply unit is used to output a DC voltage, which is then converted by an inverter to an AC voltage having a predetermined frequency so as to be applied to a load such as a motor. Such a DC power supply unit is required to have higher power-conversion efficiency to save energy.
To satisfy the requirement, a synchronous rectifier circuit including a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is proposed, such as in Japanese Patent Application Publication No. 2008-061412, for a DC power supply unit that converts AC power to DC power.